尝试使用jquery each（）函数将值放入数组时出错

Question

I have this code:

$(".categoty-add").each(function(i) {
            categories[i][0] = $(this).val();
    });

And in output i get

TypeError: can't convert undefined to object    
categories[i][0] = $(this).val();

This is my array:

    var categories = new Array(2);
    for (i = 0; i < categories . length; ++ i)
    categories [i] = new Array (2);

What's wrong?

Answer 1

There has to be two textbox with class category-add . it they are more than two then you iterator i will be assigned a value >= 2 and then you statement becomes

categories[2][0] = $(this).val();

which is out of the bounds of the array.

Answer 2

To dynamically create an array ( first time code is run), and later update it you can do this:

/* create empty array, syntax is shortcut for new Array() and just as efficient*/
var categories=[];

$(".categoty-add").each(function(i) {
   if( categories[i] ){ /* if doesn't exist will be undefined and trigger "else"*/
        /* sub array exists, just update it*/
        categories[i][0] = $(this).val();
    }else{ 
        /* create new sub array and give value to first position */
        categories[i] =[ $(this).val()];
    }
});

DEMO: http://jsfiddle.net/FFQ2s/